1. Field of Invention
The present invention relates generally to fluid flow valves and more precisely pertains to fine regulation metering valves and especially to the valves that can provide extremely precise regulation over a large range of regulated flows.
2. Description of the Prior Art
When accurate control of relatively low flow rates is required it is wide spread practice to employ needle valves for this purpose. Different types and improvements of the needle valves serves well this purpose because of the fine adjustment and accurate control provided by such valves.
For regulating extremely low flow the needle valves are used with very small orifice and literally needle type of stem—U.S. Pat. No. 5,687,949 issued to Dukas et al, U.S. Pat. No. 3,910,553 to Boylan, U.S. Pat. No. 4,311,170 to Dolan. This needle is providing gradually changeable annular space between the stem and the seat of the valve. The maximum flow is restricted by the internal diameter of the seat. Despite of other improvements like spring supported seat, aiming to stabilize the functioning—U.S. Pat. No. 4,500,068 to Ramundsen et al, it is obvious that such limited space for the flow passage can tolerate very narrow interval of low fluid flows.
The same drawback—regulation of only low flow in a narrow interval—characterizes low flow valves having regulating notches or passages such as U.S. Pat. No. 4,406,442 to Bettin et al. Even with shut-off function the valve is capable to provide regulation in a very narrow interval. The flow-dynamic resistance of those valves is high and limited by the full bore of the created orifice.
In a more complicated construction—fine grooves with adjustable length are used for regulating very low flows U.S. Pat. No. 4,495,965 and U.S. Pat. No. 4,340,234 to Ise. Despite of the claim that the valve can regulate big flow range, this range is still limited by the naturally small cross-section of the groove compared to the inlet and outlet cross-sections.
For fine adjustment of the low flow, valves utilizing flexible tubing compressed by specially shaped surfaces U.S. Pat. No. 4,171,006 to Steere Jr. and U.S. Pat. No. 2,827,919 to Rice are suggested. Drawback of those devices is the deviation of the adjusted flow at any new position due to the memory of the plastic tubing and inconsistency of the flow (due to the mechanical properties of the plastic or resin) changing with the temperature of the fluid.
Based on similar principals, valves with cone-shaped stem are also referred as needle valves U.S. Pat. No. 5,249,773 to Feld, U.S. Pat. No. 5,244,182 to Pacht, with some decreased accuracy but used with higher flow rates. Those types of cone/needle valves are more appropriate for the moderate range of flows but fail to provide fine regulation in a very low flow mode. Their highest flow rate is still limited by the bore of the orifice, which is always smaller than the full bore of the inlet/outlet of the valve therefore providing additional flow resistance.
It is known from the prior art that the valves with capability of providing full flow, or ball valves, or hollow cylinder as a stem, are well accepted to regulate roughly high flows but completely fail to provide fine regulation. One skilled in the art knows that for each range of flow, valve with different construction and respective accuracy is used. The known art does not provide a valve with fine regulation and especially metering capability for very high, moderate and very low flow ranges all together.
Objectives and Advantages
It is a primary objective of the present invention to provide a solution for smooth, fine, accurate and repeatable regulation and measuring function over a broad range of flows. The low range must start from zero and the top range is to be limited by the full-bore opening of the inlet/outlet of the valve. Such valve will provide regulation over a flows ranging up to four orders of magnitude.
Another object of the present invention is to exploit different designs having the same basic concept, functions and abilities, but serving different needs thereby to develop a family of valves having same theoretical and functional background.
Consecutively another object of the present invention is to provide easy technologically achievable solutions for manufacturing such family of valves as well as materials for building such valves. Further objects and advantages of the present invention will become apparent from consideration of the drawings and ensuing description.